OpenGL: Fix mouse-move handling for OpenGL views

Since b108fe26c3, JUCE NSViews have
ignored mouse movements for child views. However, this causes issues for
OpenGL views, which still expect to receive mouse input via the parent
view. This fix makes the inner OpenGL view effectively invisible to the
mouse, so all mouse events are handled by the owning JUCE view.

modules/juce_opengl/native/juce_OpenGL_mac.h

@@ -328,6 +328,11 @@ public:
                 return [[(NSOpenGLView*) self superview] accessibilityHitTest: p];
             });
 
+            addMethod (@selector (hitTest:), [] (id, SEL, NSPoint) -> NSView*
+            {
+                return nil;
+            });
+
             registerClass();
         }
     };